A radio-frequency identification (RFID) system uses RFID tags and interrogators. In order to interrogate a tag, an interrogator transmits an encoded radio signal to the tag. The tag receives the signal and responds with its ID signal, or code, that is stored in the tag. Because tags have unique ID signals, an interrogator can discriminate among several tags that might be within range. A tag can be either passive or active. An active tag includes a battery and periodically transmits its ID signal. A passive tag is cheaper and smaller than an active tag because a passive tag does not include a battery. Instead, a passive tag uses the radio energy transmitted by the interrogator in order to transmit its ID signal.
One popular format for an ID signal stored in a tag is a 96-bit string of data. The first eight bits are a header that identifies the version of the ID code format. The next 28 bits identify the organization that manages the data for the tag. The organization number may be assigned by a central body. The next 24 bits are an object class, identifying they type of object represented by the tag, and the last 36 bits are a unique number for a particular tag. As such, each tag has a unique ID signal.
The distance from which a tag can be read is called its read range. Read range depends on a number of factors, including the frequency of the radio waves used for communication and the power output of the interrogator. Some tags have a short read range that limits the applications in which these tags may be used.
It should be understood, however, that the specific embodiments given in the drawings and detailed description thereto do not limit the disclosure. On the contrary, they provide the foundation for one of ordinary skill to discern the alternative forms, equivalents, and modifications that are encompassed together with one or more of the given embodiments in the scope of the appended claims.